Secondary (i.e. rechargeable) electrochemical cells and batteries are a power source widely used in Information-related devices, communication devices (such as personal computers, camcorders and cellular phones) as well as in the automobile industry or in stationary power generating devices. Conventional lithium-based cells typically Include a positive electrode (also referred to as “cathode”) and a negative electrode (also referred to as “anode”) whose active materials are capable of accepting and releasing lithium ions, as well as an electrolyte arranged between the electrodes and including lithium ions.
Calcium is much more abundant in nature than lithium and, despite the high atomic weight of Ca with respect to Li, the bivalent nature of Ca means that it could in principle provide a suitable rechargeable battery material, even if it has proven difficult so far to identify suitable chemistries and Ca batteries are very underdeveloped as compared to their Li counterparts.
Issues to be addressed in developing rechargeable Ca-based batteries Include:                the capacities of some known rechargeable Ca-based batteries are relatively low;        if heated above 40° C., the electrolyte used may be subjected to decomposition in the presence of certain transition metal oxide materials typically used as positive electrode materials such as Co-based materials for example;        the operation voltages of some known rechargeable Ca-based batteries are relatively low;        reducing volume variations during cycling.        
In JP 2012-248470, Ca3Co2O6 is proposed as a positive electrode material for Ca-based batteries using V2O5 as negative electrode. The operation voltage of this battery is however relatively low.
In the Ph.D. thesis of John Rogosic entitled “Towards the Development of Calcium Ion Batteries” (MIT, 2014), V2O5, FeS2 and Mo3Se4 Chevrel phases are reported as possible positive electrode materials. The Chevrel phase is reported as the most promising material. In such a case the initial de-intercalated material has a molar mass of 600.84 g/mol. Tests are performed in a cell with the following configuration: CaHg11—CaHg/acetonitrile+Ca(ClO4)2/positive materials. The capacities (mAh/g-active positive material) achieved in this prior art are extremely low because the positive and negative materials reported have high molar weight. Also non-environmentally friendly mercury is contained. In addition, acetonitrile is highly flammable.
In Hayashi et al., Electrochemical and Solid-state Letters, 7(5), A119-A121 (2004), V2O5 is reported as possible host materials for Ca2+ ions. The accommodation of Ca2+ in the V2O5 structure takes place around −1 V vs. Ag+/Ag pseudo reference (believed to be equivalent to 2.67 V vs Ca2+/Ca). Re-chargeability is not demonstrated in this document.
In Hayashi et al., Journal of Power Sources 119-121 (2003), 617-620, V2O5 or V2O5—P2O5 are reported as possible host materials for Ca2+ ions. The accommodation of Ca2+ in the V2O5 structure takes place around −1 V vs. Ag+/Ag pseudo reference (believed to be equivalent to 2.67 V vs Ca2+/Ca). The cell configuration is Ca/electrolyte+Ca(ClO4)2/V2O5. Re-chargeability for 1 cycle is apparently observed in this system and a new phase was formed during discharge.
In US 2003/0059684, a non-aqueous electrolyte battery is disclosed whose negative electrode contains Al, Ca or Mg, and wherein the electrolytic solution uses a mixture of organic solvents, such as a lactone, acetonitrile or carbonate, and an alkyl sulfone. Fe2(SO4)3 is the main positive electrode material described in the examples, but the molar mass of Fe2(SO4)3 is already very high—even without considering the Ca2+ ions mass contribution. Theoretical capacities are not described nor the expected maximum amount of Ca2+ expected to be accommodated in the structure. The operation voltage of the various types of batteries is said to be between 1V for discharge and 3V for charge for all types of batteries containing Al, Ca or Mg.
In de la Calle et at, Journal of Solid State Chemistry 179, (2006), 1636-1641, CaMoO3 synthesis by a soft chemical route is reported. It is not used as a battery material but as a magnetic material.